Ion mobility spectrometers (IMS) came into being in the early 1970's in order to analyze and detect organic vapors in air. An ion mobility spectrometer consists of a reaction chamber for the generation of ions of substances to be analyzed and a drift chamber for separation of the ions. In the reaction chamber, for ionization of the substance to be analyzed, usually radioactive materials such as, for example, tritium, .sup.53 Ni, .sup.241 Am etc. are used. The disadvantage of such IMS is that the use of a radioactive ionization source can be dangerous to the environment and to the health of maintenance personal.
In this context there were made numerous attempts to design IMS constructions with non-radioactive ionization sources in the reaction chamber such as, for example, photoemitter to generate electrons. However, in these designs one could not exclude the contact of analyzed gas molecules with the source surface. This is one of the reasons for instabilities of detector indications because such contacts can change the operating characteristics of a non-radioactive source.
The prior art IMS consist of a reaction chamber, a drift chamber, a non-radioactive electron source installed in said reaction chamber, an input connected to said reaction chamber for supplying an analyte and an output for withdrawing said analyte, as well as a collecting electrode mounted in said drift chamber (ref. e.g. Begley P., Carbin R., Fougler B. F., Sammonds P. G., J. Chromatogr. 88 (1991) p. 239).
The disadvantage of these prior art IMS is that the analyte directly contacts the surface of the non-radioactive ionization source which in its turn changes the operating characteristics of said ionization source and may be one of the reasons for the instability of detector indications. Another disadvantage is that one cannot obtain positive ions with the help of such an ionization source.
The purpose of this invention lies in the design of an IMS construction that eliminates the contact of the analyte with the ionization source and enables one to work with positive and negative ions.